1. Field of the Invention
The present invention relates to an oscillator and an oscillation method for generating an oscillation signal used as a synchronization signal, say, during data recording or reproduction by controlling oscillation frequencies.
2. Prior Art
When data is recorded to or reproduced from a tape storage medium, an operation references a synchronization signal having a specified sampling frequency. Namely, when data is recorded to or reproduced from a tape storage medium, a recording track is written or read at a write or read timing indicated by the synchronization signal with the specified sampling frequency.
Conventionally, a signal generation circuit as shown in FIG. 5 is often used for generating synchronization signals. The-signal generation circuit in FIG. 5 adjusts signal delays and controls frequencies in buffers 103a through 103c and an inverter 104 which are connected in a ring. Thereby, the signal generation circuit uses a D/A converter (referred to hereafter as the DAC) 101 to convert a digital frequency control signal into an analog value. The converted analog value is input to current sources 102a through 102d to vary current values. Thus, the signal generation circuit controls an output timing of the generated synchronization signal to use the synchronization signal as an oscillation output.
Owing to rapid development of the integrated circuit technology in recent years, however, swift alternations are made to generations of processes for manufacturing digital LSIs (Large Scale Integrated Circuits). Each time the process changes, there has been a need for developing a new analog cell for handling analog signals as shown in FIG. 5. There arises the problem of prolonging a term for developing apparatuses including the signal generation circuit connected to the digital LSI chip and increasing manufacturing costs.
The present invention has been made in consideration of the foregoing. It is therefore an object of the present invention to provide an oscillator and an oscillation method which can decrease manufacturing costs by generating an oscillation signal without converting a digital signal to an analog signal.
An oscillator according to the present invention for solving the above-mentioned problems comprises a delay coarse adjustment circuit, a delay fine adjustment circuit, and an inverter circuit. The delay coarse adjustment circuit supplies a coarse delay to an input oscillation signal of which delay amount varies stepwise based on a delay coarse adjustment signal. The delay fine adjustment circuit supplies a fine delay to an input oscillation signal of which delay amount varies stepwise based on a delay fine adjustment signal. The fine delay is smaller than a delay amount supplied in the delay coarse adjustment circuit. The inverter circuit is supplied with the oscillation signal which passes the delay coarse adjustment circuit and the delay fine adjustment circuit. By having these circuits, the oscillator coarsely adjusts delays in the delay coarse adjustment circuit and fine adjusts delays in the delay fine adjustment circuit.
The oscillator stepwise controls an oscillation frequency of the oscillation signal by connecting the delay coarse adjustment circuit, the delay fine adjustment circuit, and the inverter circuit in a ring.
An oscillation method according to the present invention stepwise varies a delay amount in the delay coarse adjustment circuit based on the delay coarse adjustment signal and supplies a coarse delay to the oscillation signal. The oscillation method stepwise varies a delay amount in the delay fine adjustment circuit based on the delay fine adjustment signal and supplies a fine delay to the oscillation signal. The fine delay has a smaller delay amount than the coarse delay.
The oscillation method stepwise controls an oscillation frequency of the oscillation signal by letting it more than once pass the delay coarse adjustment circuit, the delay fine adjustment circuit, and the inverter circuit which are connected in a ring.
As mentioned above in detail, the oscillator according to the present invention uses the delay adjustment circuits for coarsely adjusting delays. When fine adjusting delays in the delay fine adjustment circuit, the oscillator stepwise varies coarse and fine adjustments of delays. Additionally, the oscillator stepwise controls an oscillation signal""s oscillation frequency by connecting the delay coarse adjustment circuit, the delay fine adjustment circuit, and the inverter circuit in a ring. Therefore, the oscillator can operate just by using digital signals and generate oscillation signals without converting a digital signal into an analog signal. Accordingly, the oscillator can be easily mounted on a digital LSI chip and the like and decrease manufacturing costs.
Further, an oscillation method according to the present invention stepwise varies a delay amount in the delay coarse adjustment circuit based on the delay coarse adjustment signal and supplies a coarse delay to the oscillation signal. The oscillation method stepwise varies a delay amount in the delay fine adjustment circuit based on the delay fine adjustment signal and supplies a fine delay to the oscillation signal. This time, the oscillation method stepwise varies a delay and controls an oscillation frequency of the oscillation signal by letting it more than once pass the delay coarse adjustment circuit, the delay fine adjustment circuit, and the inverter circuit which are connected in a ring. Therefore, the oscillation method can handle only digital signals and generate oscillation signals without converting a digital signal into an analog signal. Accordingly, the oscillation method can easily allow a processing block for generating oscillation signals to be mounted on a digital LSI chip and decrease manufacturing costs.